Flow control method of data service transmission in sdh network

ABSTRACT

A flow-control method for data traffic transmitted through SDH network, wherein: during data transmission through the SDH network, the EoS device generates and encapsulates LFP frames, maps the LFP frames into SDH payload, and transmits the SDH payload to the opposite device, which demaps the LFP frames from the SDH payload and executes the flow control information carried in the LFP frames; the carrier of the LFP frames may be standard PAUSE frame structure defined by 802.3x; LFP frame transparent or LFP frame regeneration may be used when the EoS device identifies LFP frames; the present invention is a high-performance method for flow control of data transmission, with high applicability and reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application derives priority from PCT International Application No.PCT/CN2003/000643, filed on Aug. 8, 2003, which designates the UnitedStates, and which derives priority from Chinese Application No.02130031.3, filed on Aug. 10, 2002, both of which are incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates to data transmission, particularly to aflow-control method for data traffic transmitted through SynchronousDigital Hierarchy (SDH) network.

BACKGROUND OF THE INVENTION

As SDH network evolves rapidly, EoS (Ethernet over SDH/SONET) technologyis used more and more widely; therefore, how to implement dataapplications through SDH network efficiently becomes a crucial issue. InEthernet transmission applications through Metropolitan Area Network(MAN), the distance between two sites can reach 1˜2 hundred km, andvirtual cascaded mapping pattern for EoS, so the time delay of datatransmission between two sites may be as high as several milliseconds oreven tens of milliseconds. In addition, Ethernet traffic has outburstfeature, i.e., instantaneous flow rate maybe very large, therefore theinstantaneous flow rate may even exceed the pre-assigned bandwidth.

Presently, a common flow-control mechanism is CAR (Committed AccessRate), i.e., in case of network congestion, the data beyond the CAR willbe discarded by using priority or others like. A disadvantage of thecontrol mechanism is that it often results in severe packet loss, whichwill severely degrade network performance in common TCP/IP applications;especially for the TCP/IP protocol that is extensively used, packet losswill result in severely degraded application performance. For example,suppose 10M/b Ethernet devices are used in a TCP application and theAckTime is set as 5s, Frame Loss Ratio (FLR) 1% will result inserviceability degraded by 98% for 1,500-Byte Ethernet frames.

In some EoS devices, the PAUSE frames generated at a user data devicemay be transferred to the opposite user data device; however, such datatransmission devices directly transfer PAUSE frames generated by userdata devices, and said method is only suitable for short distanceinstead of long distance because said PAUSE frames will be delayedduring transmission; in addition, if the user device at either enddoesn't support PAUSE frames, said method can't be used.

As shown in FIG. 1, the EoS device comprises 3 parts: Ethernet accessparts, which comprise Physical Layer (PHY) and Media Access Control(MAC); encapsulating and decapsulating parts, the encapsulation may beLAPS (Link Access Protocol-SDH), HDLC (High Level Data Link Control), orGFP (General Framing Procedure), and mapping and demapping parts, themapping method may be virtual cascading or cascading.

Suppose the bandwidth of SDH network is 1 VC3 (i.e., 45M at maximum), ifthe data transmitting rate of user data device A exceeds 1 VC3, theresidue Ethernet frames are stacked at the encapsulating part A becausethe flow at Mapping part A is constant (1 VC3) according to the priorart; when the cache of encapsulating part A is used up, the data in MACA can't be sent to encapsulating part A any more; therefore, if Ethernetflow control is enabled, PHY+MAC A will send PAUSE frames (full duplex)or back pressure (half duplex) to user device, shown as the dotted line1 in FIG. 1 (if Ethernet flow control is disabled, MAC A will discardthe residue Ethernet frames, referring to IEEE802.3x document forEthernet flow control), as a result, the transmitting speed of device Awill be decreased to below 1 VC3 to prevent packet loss and severelydegraded network performance.

If the transmitting speed of device A is lower than 1 VC3 but thereceiving speed of device B is less than the transmitting speed ofdevice A due to certain reasons (for example, device B is attached witha plurality of 10M devices but only one of them is working), the trafficfrom device A to the transmitting end of EoS device B will not beblocked, instead, device B will be blocked; thus, according to thespecification in 802.3x, device B will send 802.3x flow-controlinformation (may be PAUSE frames or back pressure signals) to ports ofthe EoS device, which is directly connected to it (i.e., the dotted line2 in FIG. 1); according to the specification in 802.3x, the flow-controlinformation will be terminated by MAC B instead of being transferred todevice A; at the same time, MAC B will stop sending data to device B,but device A continues sending data at original speed, thus the Ethernetframes from device A stack up at the decapsulating part B or MAC B; whenthe caches at these positions are used up, packet loss will surely occurat EoS #B; therefore, though both device A and device B are 802.3xEthernet flow control-supporting devices, packet loss is inevitableafter the EoS device. It indicates that traditional 802.3x-basedtechnical solution is unable to ensure Ethernet flow control with EoSdevices.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a high-performanceflow-control method for data traffic transmitted through SDH network torealize lossless transparent transmission of Ethernet data through SDHnetwork.

According to the present invention, a flow-control method for datatraffic transmitted through SDH network comprises the following steps:

-   -   A. During data transmission through SDH network, the EoS        processing device creating and encapsulating LFP (Line        Flow-Control Protocol) frames according to the utilization        condition of the frame cache inside;    -   B. Said LFP frames being mapped to SDH payload as common data        frames and transferred to the opposite device;    -   C. Said opposite device demapping the SDH payload, and the EoS        processing device identifying said LFP frames and phrasing and        executing flow control information in the LFP frames.

Said step of creating and encapsulating LFP frames further comprises thefollowing steps:

A1. In the uplink direction of said EoS device, the EoS processingdevice keeping on monitoring the data volume in the cache inside andcreating LFP frames with corresponding control field; if the data volumeexceeds the upper threshold, said encapsulating part periodicallysending LFP frames, the control field of which controls to stop sending;if the data volume is lower than the lower threshold, said encapsulatingpart periodically sending LFP frames, the control field of whichcontrols to start sending; if the data volume is between the lowerthreshold and the upper threshold, said encapsulating part stops sendingLFP frames;

A2. Said LFP frames are inserted in the head of the data queue to beencapsulated and is given the priority to encapsulate; if no Ethernetframes are being encapsulated, said LFP frames are encapsulatedimmediately; otherwise they are encapsulated immediately after thecurrent Ethernet frames are encapsulated.

The carrier of LFP frames can be configured as standard PAUSE framestructure defined by 802.3x .

The advantage of the present invention is: through LFP frames, flowcontrol information is transferred between EoS devices through the SDHnetwork; the EoS devices generate LFP frames and transfer network flowcontrol information between each other so as to achieve losslesstransmission of outburst Ethernet data in the SDH network that transmitdata periodically, in order to significantly enhance the performance ofdata applications. The present invention enables transmission of flowcontrol information between EoS devices and also support full duplex orhalf duplex devices attached to EoS devices, for example, a full duplexdevice may be attached to one end of the EoS device, and a half duplexdevice may be attached to the other end of the EoS device, or halfduplex devices may be attached to both ends of the EoS device; The EoSprocessing device keeps on monitoring the data volume in the cache toavoid flow control failure due to some reasons such as LFP frametransmission failures; therefore, the present invention is ahigh-performance flow-control method for data traffic transmittedthrough SDH network and has high applicability and reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of flow control implemented according tothe prior art.

FIG. 2 is a schematic diagram of LFP process according to the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described in further detail with referenceto the following embodiments and the drawings. The present inventionwill be described with the example of A-B data transmission; theprocessing method for B-A data transmission is similar.

In the present invention, during the data transmission through SDHnetwork, the EoS devices transfer flow-control information through LFPframes between them; the carrier of LFP frames can be configured asstandard PAUSE frame structure defined by 802.3x.

During SDH mapping, the mapping part of EoS device processes bothEthernet frames and LFP frames as common data frames; the control fieldof said LFP frames is 0x0FFFFH or 0x0H and is controlled in a Xon/Xoffcontrol way.

In addition, because time delay will be generated during LFP frametransmission, appropriate caches are required to compensate the timedelay; the LFP frames are implemented on the basis of in-bandmanagement, i.e., LFP frames and common Ethernet data frames aretransferred through the same transmission paths.

As shown in FIG. 2, in the uplink direction, i.e., the system direction,e.g., the direction of EoS#A-SDH network in FIG. 2, take an example forEoS#A, the EoS processing device, according to the lower/upper thresholdof frame cache (reflecting utilization of cache), will generate LFPframes, the control field of which is 0x0FFFFH or 0x0H; said LFP framesare processed as common Ethernet data frames in the mapping part of theEoS processing device; however, to enhance the performance of LFP, thepriority is given to the LFP frames to send to the mapping part of theEoS processing device; in the downlink direction i.e., the direction touser device, e.g., the direction of SDH-EoS#B in FIG. 2, the EoSprocessing device identifies the LFP frames; if the LFP frames aredetected, it explains and executes the flow-control information carriedin said LFP frames.

If the receiving end (i.e., “AR” shown in FIG. 2) of user deviceattached to EOS#A is blocked, the data volume in cache A will increasebecause the demapping part A continues working normally; when the datavolume reaches to the preset upper threshold, the EoS device A willgenerate LFP frames, the control field of which is 0x0FFFFH, and saidLFP frames are inserted in the head of data queue at the encapsulatingpart A and is given the priority to encapsulate. The process is: ifthere is no Ethernet frames being encapsulated at the encapsulating partA, said LFP frames will be encapsulated immediately; otherwise said LFPframes will be encapsulated immediately after the current Ethernet frameis encapsulated; then the encapsulated LFP frames will be mapped,transferred from the SDH network and the demapping part B to thedecapsulating part B, which identifies the LFP frames and processes itin either of the following ways:

-   -   1. LFP transparent: This way is suitable for the case in which        the network delay is small and the distance between two sites is        short. In this way, the EoS device B will phrase and execute the        LFP frames according to the characteristic of the data device        (full duplex or half duplex) attached to it.

If the user device B attached to the EoS device B works in full duplexmode, the LFP frames will not be phrased, instead, the LFP frames willbe directly transferred to the user data device B; the detailed processis: if the decapsulating part B isn't sending data to the Ethernetaccess part BR, it will send the LFP frames immediately to the Ethernetaccess part BR; otherwise it will send the LFP frames immediately afterthe current Ethernet data is sent, in this case, the LFP frames will notpass through cache B in order to enhance its performance.

If the user data device B attached to the EoS device B works in halfduplex mode, the control field of the LFP frames should be phrased,i.e., if it is 0x0H, the back pressure control signal will be canceled;otherwise the back pressure control signal will be sent to make the userdevice B attached to EOS#B detect a conflict and thus stop transmittingEthernet data to the EoS device B.

2. LFP Regeneration: The EoS device B phrases and executes the LFPframes; if the control field of the LFP frames is not 0x0H, i.e., theEoS device is disabled from sending data, the encapsulating part willstop working, i.e., it stops receiving data from Ethernet access partBT; hower, if the EoS B device itself generates LFP frames at this time,the encapsulating part B still forwards the LFP frames to the mappingpart B, i.e., in any cases, the LFP frames shall be forward to themapping part via the encapsulating part. Thus the data from Ethernetaccess part BT will stack up at the encapsulating part B and willfinally cause the user device B stopping sending Ethernet framesaccording to 802.3x Ethernet flow control protocol, i.e., no data willbe transmitted to BT; if the control field of the LFP frames is 0x0H,i.e., the EoS device is enabled to send data, the encapsulating part Bwill work normally, and encapsulate and send Ethernet frames from theEthernet access part BT to the mapping part B.

In this mode, the devices attached to EoS devices at both ends of theSDH network are not required to work in full duplex; instead, they areonly required to support standard 802.3x flow control operation. That isto say, the user device at one end may work in full duplex mode whilethe device at the other end may work in half duplex mode; or the devicesat both ends may work in half duplex mode.

After the user device B attached to EOS#B stops sending data to EOS#B,i.e., there is no Ethernet frame input at BT, the data volume in cache Aof EOS#A will be reduced gradually; when the data volume reaches to thelower threshold, the decapsulating part A will generate LFP frames, thecontrol field of which is 0x0H; said LFP frames are given the priorityto send to the decapsulating part B in EOS#B and is phrased andexecuted; as a result, the user device B attached to EOS#B will senddata again.

In order to avoid LFP control failure due to accidents such as LFP frametransmission failures, the EoS processing device keeps on monitoring thedata volume in the cache; when the data volume exceeds the upperthreshold or is lower than the lower threshold, the EoS processingdevice will periodically send LFP frames with corresponding controlfield; if the data volume is between the upper threshold and the lowerthreshold, the EoS processing device will stop sending LFP frames; ifthe data volume exceeds the upper threshold, it will periodically sendLFP frames, the control field of which is 0x0FFFFH; if the data volumeis lower than the lower threshold, it will periodically send LFP frames,the control field of which is 0x0H.

The lower, upper thresholds and time intervals are configurable, and thetime intervals may be different to each other. It is recommended thatthe time interval for resending LFP frames with the control field0x0FFFFH should not be too long and the time interval for resending LFPframes with the control field 0x0H should not be too short, so as toavoid excessive occupation of available bandwidth.

Presently, the format of LFP frames is identical to that of standard802.3x PAUSE frame in order to simplify LFP frame transparent scheme;however, other formats may also be acceptable if corresponding formatconversion at the receiving end in LFP transparent mode is performed; asfor LFP frame regeneration scheme, format conversion is unnecessarybecause the LFP frames are only transferred between EoS devices.

The present invention is also applicable to SONET network, and theprinciple and control process are similar. So the case in which thepresent invention is applied to SONET network will not be describedhere.

1-7. (canceled)
 8. A flow-control method for data traffic transmittedthrough a synchronous digital hierarchy (SDH) network, comprising:creating and encapsulating, during data transmission through said SDHnetwork, one or more line flow-control protocol (LFP) frames, accordingto a utilization condition of a frame cache of a first Ethernet overSDH/SONET (EoS) device coupled to said SDH network, wherein each LFPframe is mapped to an SDH payload as a common data frame; transferringsaid one or more LFP frames to a second EoS device coupled to said SDHnetwork; demapping the SDH payload at said second EoS device;identifying said one or more LFP frames at said second EoS device; andphrasing and executing flow-control information contained in said one ormore LFP frames at said second EoS device.
 9. The flow-control methodaccording to claim 8, wherein said creating and encapsulating comprises:continuing to monitor data volume in an uplink direction in said framecache of said first EoS device; inserting a control field into each ofsaid one or more LFP frames, said control field being based upon saiddata volume in said frame cache, wherein: if said data volume exceeds anupper threshold, said encapsulating includes periodically sending LFPframes whose control field controls to stop sending; if said data volumefalls below a lower threshold, said encapsulating includes periodicallysending LFP frames whose control field controls to start sending; and ifsaid data volume falls between said upper threshold and said lowerthreshold, said encapsulating does not send LFP frames; and wherein saidone or more LFP frames are inserted at the head of a data queue forencapsulation and are given priority, and wherein if there are noEthernet frames being encapsulated, the LFP frames are immediatelyencapsulated, and otherwise, the LFP frames are encapsulated immediatelyafter current Ethernet frames are encapsulated.
 10. The flow-controlmethod according to claim 9, wherein a carrier for LFP frames isconfigured according to a standard IEEE 802.3x PAUSE frame structure.11. The flow-control method according to claim 9, wherein if said datavolume exceeds said upper threshold, the control field will contain0x0FFFFH, and if said data volume falls below said lower threshold, thecontrol field will contain 0x0H; and wherein said control field iscontrolled in an Xon/Xoff fashion.
 12. The flow-control method accordingto claim 8, wherein a carrier for LFP frames is configured according toa standard IEEE 802.3x PAUSE frame structure.
 13. The flow-controlmethod according to claim 8, wherein said second EoS device processessaid LFP frames in an LFP frame regeneration pattern, said framing andexecuting comprising: if the control field in an LFP frame does notcontrol to start sending, halting encapsulating of data at said secondEoS device to cause data to stack up and to cause a user device coupledto said second EoS device to stop sending Ethernet frames, said LFPframe being defined by IEEE 802.3x as a PAUSE frame or a back pressuresignal; and if the control field in an LFP frame controls to startsending, continuing to normally encapsulate and map data at said secondEoS device.
 14. The flow-control method according to claim 13, whereinwhen said user device coupled to said second EoS device stops sendingdata to said second EoS device, the data volume in the data cache ofsaid first EoS device decreases gradually; wherein when the data volumein the data cache of said first EoS device reaches said lower threshold,the first EoS device generates at least one LFP frame having a controlfield to start sending; and wherein said LFP frames are given priorityfor decapsulation at said second EoS device to phrase and executeflow-control to control the user device coupled to said second EoSdevice to send data again.
 15. The flow-control method according toclaim 8, wherein an LFP transparent pattern is used when said second EoSdevice identifies and processes an LFP frame; and wherein said secondEoS device explains and executes said LFP frames according to whethersaid user device coupled to said second EoS device supports full duplex,wherein: if said user device works in full duplex mode, it isunnecessary to phrase the LFP frames, and the LFP frames are sentdirectly to said user device; and if said user device works in halfduplex mode, the control field of each LFP frame is phrased, wherein ifthe control field controls to start sending, a back pressure controlsignal will be cancelled, and otherwise, the back pressure controlsignal will be sent to make said user device detect a conflict and stoptransmitting data.
 16. The flow-control method according to claim 15,wherein when said user device coupled to said second EoS device stopssending data to said second EoS device, the data volume in the datacache of said first EoS device decreases gradually; wherein when thedata volume in the data cache of said first EoS device reaches saidlower threshold, the first EoS device generates at least one LFP framehaving a control field to start sending; and wherein said LFP frames aregiven priority for decapsulation at said second EoS device to phrase andexecute flow-control to control the user device coupled to said secondEoS device to send data again.
 17. A flow-control method for datatraffic transmitted through a synchronous digital hierarchy (SDH)network, comprising: monitoring, at a first device coupled to said SDHnetwork, a receive data cache to determine a data volume in said receivedata cache; comparing said data volume to a predetermined upperthreshold and a predetermined lower threshold; creating and transmittingone or more flow-control frames to a second device coupled to said SDHnetwork if said data volume is not between said upper threshold and saidlower threshold, wherein if said data volume is greater than said upperthreshold, at least one of said flow-control frames contains a controlfield to control said second device to stop transmitting data, and whereif said data volume is less than said lower threshold, at least one ofsaid flow-control frames contains a control field to control said seconddevice to start sending data.
 18. The flow-control method according toclaim 17, wherein each of said first and second devices comprises anEthernet over SDH/SONET (EoS) device.
 19. The flow-control methodaccording to claim 17, wherein a carrier of said flow-control frames isconfigured to have a PAUSE frame structure defined under the IEEE 802.3xstandard.
 20. The flow-control method according to claim 17, whereinsaid control field to stop transmitting data comprises 0x0FFFFH and saidcontrol filed to start sending data comprises 0x0H.
 21. The flow-controlmethod according to claim 20, wherein Xon/Xoff control is used tocontrol said control field.
 22. The flow-control method according toclaim 17, wherein said creating and transmitting one or moreflow-control frames includes: encapsulating control information; andmapping a result of said encapsulating.
 23. The flow-control methodaccording to claim 22, wherein said encapsulating control informationcomprises: encapsulating at least one said flow-control frame beforeencapsulating any other frames unless there are data frames in theprocess of being encapsulated, in which case the at least one saidflow-control frame is encapsulated immediately following encapsulatingsaid data frames.
 24. The flow-control method according to claim 17,wherein said creating and transmitting one or more flow-control framesincludes: periodically transmitting flow-control frames to control saidsecond device to stop transmitting data, as long as said data volumeremains above said upper threshold.
 25. A flow-control method for datatraffic transmitted through a synchronous digital hierarchy (SDH)network, comprising: receiving, at a first device coupled to said SDHnetwork, one or more flow-control frames from a second device coupled tosaid SDH network, wherein each flow-control frame contains a controlfield that controls a data device coupled to said first device to eitherstop sending data or start sending data, where said control field isselected based on a comparison of a data volume in a receive cache ofsaid second device to predetermined upper and lower thresholds; andprocessing said one or more flow-control frames at said first device tocontrol a data device coupled to said first device to stop transmittingdata or start transmitting data.
 26. The flow-control method accordingto claim 25, wherein said processing comprises: identifying the one ormore flow-control frames; and processing the one or more flow-controlframes in a transparent manner according to whether the data devicecoupled to said first device operates in a full-duplex mode or ahalf-duplex mode, wherein: if the data device coupled to said firstdevice operates in a full-duplex mode, each of said one or moreflow-control frames is transferred directly to the data device; and ifthe data device coupled to said first device operates in a half-duplexmode, the first device executes a control function indicated by the oneor more flow-control frames.
 27. The flow-control method according toclaim 26, wherein when said first device executes a control functionindicated by the one or more flow control frames, executing the controlfunction causes the first device to either transmit or to refrain fromtransmitting a back pressure signal to said data device.
 28. Theflow-control method according to claim 25, wherein said processingcomprises: identifying the one or more flow-control frames; andprocessing the one or more flow-control frames in a regenerative manner.29. The flow-control method according to claim 28, wherein saidprocessing the one or more flow-control frames in a regenerative mannercomprises: ceasing to receive data from said data device by said firstdevice if a flow-control frame received from said second deviceindicates to control said data device to stop transmitting; and normallyprocessing data from said data device by said first device if aflow-control frame received from said second device indicates to controlsaid data device to start transmitting.